This invention relates to the control of temperature. More specifically, this invention relates to the control of the temperature of electrical, electronic or optical devices in order to provide high levels of stability to those devices.
Optical devices and analogous electrical and electronic devices often require to be operated under very stable temperature conditions. The temperature of operation is usually set to be a little higher than the ambient temperature. For example, the operating temperature may be 75xc2x0 C. for a device operating in an external environment which temperature ranges from 0xc2x0 C. to 70xc2x0 C.
Often, the temperature of such a device must be controlled to remain within xc2x10.2xc2x0 C. of the required temperature of operation (i.e. 75xc2x0 C.), and preferably within xc2x10.1xc2x0 C. In addition to this, the temperature control must be able to accommodate wide and rapid external fluctuations within the ambient temperature range. Furthermore, a temperature controller provided to control such a device may be subject to the same, or a similar, ambient temperature as the device requiring control.
At present, the control of the temperature of a device, for the sake of example, an optical device, is achievable within a range of approximately xc2x1xc2x0C. of the temperature required for the correct operation of the device. Such a degree of control is acceptable for a device comprising optical waveguides formed in silica (SiO2) on a substrate of silicon (Si), for example.
However, the above degree of control is insufficient for the control of the temperature of optical devices comprising optical waveguides formed in silicon. If such a degree of control is utilised, the temperature will deviate too far from the ideal operating temperature of the device, and degradation in the performance of the device will ensue. There is thus a problem in the provision of a sufficient degree of control for optical devices utilising silicon waveguides and the like, and analogous electrical and electronic systems which require a similarly stable operating temperature.
With the foregoing in mind, the present invention aims to provide a greater degree of temperature control than is currently available utilising prior art temperature control circuitry and apparatus.
In accordance with the present invention there is provided a two-stage circuit configured to control the temperature of a device, comprising:
a first stage connected to the device for controlling the temperature of the device; and
a second stage comprising a temperature sensor and a heat source and/or a cooler associated with the first stage for controlling the temperature of the first stage.
The use of two stages of temperature control provides significant advantages over the prior art use of a single stage of control. The main advantage is that, by controlling the temperature of a first stage of control utilising a second stage of control, that first stage of control is able to provide an increased degree of control over the device to which the overall temperature controller is applied.
In accordance with a preferred embodiment of the present invention a heat source and temperature sensor associated with the first temperature control stage are packaged with the device which temperature is to be controlled, thereby enabling the control of the device temperature by the first temperature controller.
In accordance with a preferred embodiment of the present invention, the heat source and temperature sensor associated with the second stage temperature control circuit are packaged with the first stage temperature control circuit, thereby enabling control of the temperature of the first stage temperature control circuit.
Preferably, the first stage temperature control circuit is packaged with the device which temperature is to be controlled. This enables the provision of a more compact piece of apparatus. However, it is foreseen that the first temperature control circuit may be provided packaged separately from the device which temperature is to be controlled.
In accordance with a further preferred embodiment of the present invention, the circuit further comprises a power amplifier connected to the output of each temperature control circuit.
Preferably, each heat sensor is one of a thermistor or a resistive temperature detector (RTD).
Preferably the temperature control circuit comprises a reference voltage generator, a voltage divider, a balancing arrangement, and an amplifier circuit, and is configured to balance a sensor temperature with a required temperature. More preferably, the voltage divider is connected to the reference voltage generator thereby providing a trimming facility to tune the balance of the circuit. Still more preferably, the power amplifier provides, from the balance signal output by the temperature control circuit, a current to drive the source of heat associated with the temperature control circuit connected to the power amplifier.
Also in accordance with the present invention there is provided a method of controlling the temperature of a device which temperature requires strict control in a predetermined temperature range, comprising:
utilising a second temperature control circuit to control the temperature of a first temperature control circuit to be within a first range; and
utilising the first temperature control circuit to control the temperature of the device to be within a second range.
Preferably, the first range is about xc2x11xc2x0 C. around a desired temperature.
Preferably the second range is about xc2x10 2xc2x0 C. around a desired temperature. More preferably, the second range is about xc2x10 1xc2x0 C. around a desired temperature.